The present invention relates, in general, to packaging, and more particularly, to methods of forming leadframes and semiconductor packages.
In the past, various methods were utilized to manufacture both semiconductor packages and the leadframes utilized in manufacturing the semiconductor packages. One leadframe manufacturing method produced a leadframe having a dam-bar that extended laterally between the leads and that was connected to each lead of the leadframe. When the leadframe was molded into a package, the dam-bar was intended to prevent the molding compound from reaching the package leads. The dam-bar had to be positioned sufficiently far from the package body to leave room to excise the dam-bar without damaging the package body. The large space between the package body and the dam-bar allowed the mold material to escape and fill the space. The material also attached to the side of the leads.
Another method produced a leadframe that did not have a dam-bar. The molding equipment or mold that was utilized to produce the semiconductor package had channels or recesses into which the leads were placed. During the molding operation, mold material often traveled through the channels and attached to the sides of the leads. This mold material often is referred to as flash or flashing.
The flashing that resulted from these processes had to be removed from the leads after the molding operations were complete. In some cases, the flashing was along the entire length of the lead and could be up to 0.15 milli-meters thick. Flash removal procedures included using a high-pressure jet of water or of particles or a chemical jet to remove the flashing. The pressure often was in the range of about two hundred fifty to four hundred twenty five Kilo-grams/square centi-meter (250-425 KGm/cm2).
As the size of semiconductor packages and leads for the packages continued to decrease, the leads and the packages became more delicate and more easily damaged. The smaller lead and package sizes made it more difficult to prevent the mold material from escaping the mold cavities, thus, made it more difficult to keep the mold material from adhering to the leads. In some cases the flashing was longer than the finished lead length and could be thicker than the lead width. This made flashing removal very difficult. Additionally, the smaller lead and package size made it more difficult to remove the flashing without damaging the leads and the packages.
Accordingly, it is desirable to have a leadframe having small leads, that reduces the amount of mold material escaping from the mold cavity and along the leads, that reduces the amount of mold material or flashing adhering to the leads, and that minimizes lead damage during flashing removal.
For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well known steps and elements are omitted for simplicity of the description.